Tool
RSU vest & withholding-gap calculator
Map out your vest schedule, see the estimated value of each vest, and check whether the flat 22% federal supplemental withholding could fall short of your own marginal rate. Nothing you type is stored or sent anywhere.
Not sure of your marginal rate? It's the federal bracket your last dollar of income falls into. This tool is federal-only — see the notes below the results.
| Vest date | Shares | Gross | Withheld | Est. gap |
|---|---|---|---|---|
| 2026-10-29 | 250 | $37,500 | $8,250 | $3,750 |
| 2027-01-29 | 250 | $37,500 | $8,250 | $3,750 |
| 2027-04-29 | 250 | $37,500 | $8,250 | $3,750 |
| 2027-07-29 | 250 | $37,500 | $8,250 | $3,750 |
| 2027-10-29 | 250 | $37,500 | $8,250 | $3,750 |
| 2028-01-29 | 250 | $37,500 | $8,250 | $3,750 |
| 2028-04-29 | 250 | $37,500 | $8,250 | $3,750 |
| 2028-07-29 | 250 | $37,500 | $8,250 | $3,750 |
| 2028-10-29 | 250 | $37,500 | $8,250 | $3,750 |
| 2029-01-29 | 250 | $37,500 | $8,250 | $3,750 |
| 2029-04-29 | 250 | $37,500 | $8,250 | $3,750 |
| 2029-07-29 | 250 | $37,500 | $8,250 | $3,750 |
Showing the first 12 of 16 vests — totals above cover the whole schedule.
About these numbers
- Rough estimate for education only — not tax advice.
- Federal flat-rate math only: ignores state and local tax, Social Security and Medicare (FICA), the Additional Medicare Tax, NIIT, AMT, deductions, credits, and phaseouts.
- Assumes every vest is withheld at the flat supplemental rate; your employer's actual withholding may differ (e.g. 37% above $1M of supplemental wages).
- Uses the share price you entered for every vest — actual vest-day prices will differ.
- Consult a CPA or tax professional about your actual situation.
Track it automatically
Forth Arc puts your RSU grants on your real balance sheet — every projected vest, recorded vests with actual proceeds, and side-by-side scenario comparisons — free.
Create a free accountWhat is an RSU vest?
Restricted stock units (RSUs) are company shares granted on a schedule. On each vest date a portion of the grant becomes yours, and its market value on that day is taxed as ordinary income — most employers withhold a flat federal "supplemental wages" rate on it.
Why can the flat 22% withholding fall short?
The default federal supplemental withholding rate is 22%, but vest income stacks on top of salary — so for many people the vest's last dollars fall in a higher bracket (24%, 32%, 35%, or 37%). The difference between what was withheld and what the income is taxed at can become a balance due at filing time. This page shows that difference as an estimate so the number isn't a surprise; what to do about it is between you and your tax professional.
Is my data stored?
No. Nothing you type here is sent to or stored on our servers.